Implantable medical device having multiple electrode/sensor capability and stimulation based on sensed intrinsic activity

ABSTRACT

In one embodiment, an implantable neurostimulator comprises a pulse generator that generates an electrical pulse signal to stimulate a neural structure in a patient, a stimulation lead assembly coupled to the pulse generator for delivering the electrical pulse signal to the neural structure, a plurality of sensors coupled to the pulse generator, and sensor select logic. Each sensor is individually selectable and the sensor select logic selects any two or more of the plurality of sensors for sensing a voltage difference between the selected sensors. In other embodiments, two or more physiologic parameters are sensed. In yet another embodiment, a method comprises sensing intrinsic electrical activity on a person&#39;s nerve and stimulating the nerve based on the sensed intrinsic electrical activity of the nerve.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. patent application Ser. No.11/045,602, entitled “Implantable Medical Device Having MultipleElectrode/Sensor Capability And Stimulation Based On Sensed IntrinsicActivity,” filed Jan. 27, 2005, the contents of which are herebyincorporated by reference in its entirety.

BACKGROUND

1. Technical Field

The disclosed subject matter relates generally to implantable medicaldevices and more particularly to implantable medical devices that areadaptable to one or more physiological conditions in a patient in whichthe devices are implanted.

2. Background Information

Various diseases and disorders of the nervous system are associated withabnormal neural discharge patterns. One treatment regimen for suchdiseases and disorders includes drug therapy. Another treatmenttechnique includes the implantation in the patient of an implantablemedical device that comprises a pulse generator for electricallystimulating a target location of the patient's neural tissue. In onesuch available treatment for epilepsy, the vagus nerve is electricallystimulated by a neurostimulator device substantially as described in oneor more of U.S. Pat. Nos. 4,702,254, 4,867,164, and 5,025,807, all ofwhich are incorporated herein by reference.

Some implantable pulse generators used for electrical stimulation ofneurological tissue operate according to a therapy algorithm programmedinto the device by a health care provider such as a physician. One ormore parameters of the therapy may thereafter be changed byreprogramming the neurostimulator after implantation by transcutaneouscommunication between an external programming device and the implantedneurostimulator. The ability to program (and later re-program) theimplanted device permits a health care provider to customize the therapyprovided by the implanted device to the patient's needs, and to updatethe therapy periodically should those needs change.

It is desirable, however, for an implantable medical device, such as aneurostimulator, to be able to automatically detect the onset of one ormore physiological parameters, particularly where the parameter(s)indicate the actual or impending occurrence of an undesirablephysiological event, such as an epileptic seizure, and then initiate atherapeutic response specifically tailored to the physiologicalparameters detected in the body of the individual patient to mitigate orprevent the physiological event without the necessity of intervention bya health care provider. Detection of such physiological events is,however, complicated by physiological differences among patients.Improvements in this area are desirable.

BRIEF SUMMARY

Various apparatus and method embodiments of the invention are describedherein. For example, in one embodiment of the invention, an implantableneurostimulator comprises a pulse generator that generates an electricalpulse signal to stimulate a neural structure in a patient, a stimulationlead assembly coupled to the pulse generator for delivering theelectrical pulse signal to the neural structure, a plurality of sensorscoupled to the pulse generator, and sensor select logic. Each sensor isindividually selectable and the sensor select logic selects any two ormore of the plurality of sensors for sensing a voltage differencebetween the selected sensors.

In another embodiment, an implantable neurostimulator comprises a pulsegenerator that generates an electrical pulse signal to stimulate acranial nerve in a patient, a stimulation lead assembly, and a pluralityof sensor elements. The sensor elements may be coupled to the pulsegenerator and sense at least two physiological parameters selected fromthe group consisting of an action potential in a nerve tissue, a heartparameter, a temperature, a blood parameter, and brain wave activity.

In yet another embodiment, an implantable neurostimulator comprises apulse generator, a stimulation lead assembly, a plurality of sensorelements coupled to the pulse generator for sensing at least twophysiological parameters selected from the group consisting of an actionpotential in a nerve tissue, a heart parameter, a temperature, a bloodparameter, and brain wave activity, each of the sensor elements adaptedto provide a sensor signal, and a controller. The controller receivesand analyzes sensor signals from the sensor elements. The pulsegenerator generates the electrical pulse signal to provide therapeuticneurostimulation to the patient in response to the controller'sanalysis.

In another embodiment, a method comprises receiving sensor signals fromat least two sensors in a patient and performing an analysis based onthe at least two sensor signals to determine whether electricalneurostimulation is needed. The method further comprises providing anelectrical pulse to a nerve in the patient when it is determined thatelectrical neurostimulation is needed.

In yet another embodiment, a method comprises sensing at least twophysiological parameters selected from the group consisting of voltagefluctuations in a nerve tissue, a heart parameter, a temperature, ablood parameter, and brain wave activity. The method also comprisesperforming an analysis based on the at least two sensed physiologicalparameters to determine whether electrical neurostimulation is neededand providing an electrical pulse to a nerve in the patient when it isdetermined that electrical neurostimulation is needed.

In yet another embodiment, a method (and associated apparatus) comprisessensing intrinsic electrical activity on a person's nerve andstimulating the nerve based on the sensed intrinsic electrical activityof the nerve. This embodiment may be for either blocking intrinsicelectrical activity from reaching the brain or to increase the efficacyof vagus nerve stimulation.

These and other embodiments are disclosed herein. The preferredembodiments described herein do not limit the scope of this disclosure.

Notation and Nomenclature

Certain terms are used throughout the following description and claimsto refer to particular system components. Persons skilled in the artwill appreciate that components may be denoted in the art by differentnames. The present invention includes within its scope all components,however denoted in the art, that achieve the same function. In thefollowing discussion and in the claims, the terms “including” and“comprising” are used in an open-ended fashion, and thus should beinterpreted to mean “including, but not limited to.” Also, the terms“couple,” “couples” or “coupled” are intended to refer to either anindirect or direct connection. Thus, if a first device couples to asecond device, that connection may be through a direct connection, orthrough an indirect connection via other devices and connections.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more detailed description of the preferred embodiments of thepresent invention, reference will now be made to the accompanyingdrawings, wherein:

Figure I depicts, in schematic form, an implantable medical device, inaccordance with a preferred embodiment of the invention, implantedwithin a patient and programmable by an external programming system;

FIG. 2 is a block diagram of the implantable medical device of FIG. 1and comprising a stimulation, sensing and communication unit;

FIG. 3 is a block diagram of the stimulation, sensing and communicationunit of FIG. 2;

FIG. 4 is a flow chart depicting an exemplary method for determining oneor more markers in a patient's physiologically parameters indicative ofthe occurrence or impending occurrence of a physiological event;

FIG. 5 is a flow chart illustrating the use of the marker(s) to predictor detect the onset of a physiological event;

FIG. 6 is a flow chart illustrating an embodiment of adjusting one ormore stimulation parameters to elicit an evoked response;

FIG. 7 is a flow chart illustrating an embodiment of adjusting one ormore stimulation parameters to determine a stimulation ceiling for anevoked response;

FIG. 8 is a flow chart illustrating an embodiment of adjusting one ormore stimulation parameters to induce an action potential in one or moretarget vagus nerve fibers;

FIG. 9 is a flow chart illustrating an embodiment of adjusting one ormore stimulation parameters to excite target tissue while reducingexcitation of non-targeted tissue; and

FIG. 10 is a flow chart illustrating an embodiment of stimulating inresponse to intrinsic electrical activity.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is susceptible to implementation in variousembodiments. The disclosure of specific embodiments, including preferredembodiments, is not intended to limit the scope of the invention asclaimed unless expressly specified. In addition, persons skilled in theart will understand that the invention has broad application.Accordingly, the discussion of particular embodiments is meant only tobe exemplary, and does not imply that the scope of the disclosure,including the claims, is limited to specifically disclosed embodiments.

FIG. 1 illustrates an implantable medical device (“IMD”) 10 implanted ina patient. The IMD 10 may be representative of any of a variety ofmedical devices. At least one preferred embodiment of the IMD 10comprises a neurostimulator for stimulating a neural structure in apatient, particularly a neurostimulator for stimulating a patient'scranial nerve such as a vagus nerve 13. Although the device 10 isdescribed below in terms of vagus nerve stimulation (“VNS”), thedisclosure and claims that follow are not limited to VNS, and may beapplied to the stimulation of other cranial nerves such as thetrigeminal and/or glossopharyngeal nerves, or to other neural tissuesuch as one or more brain structures of the patient, spinal nerves, andother spinal structures.

Referring still to FIG. 1, a lead assembly comprising one or more leads16 is coupled to the IMD 10 and includes one or more electrodes, such aselectrodes 12 and 14. Each lead has a proximal end that connects to theIMD 10 and a distal end on which one or more electrodes are provided. Atleast one electrode, and preferably an electrode pair, is used as astimulating electrode to deliver electrical current to target tissuessuch as the patient's vagus nerve 13. Further, at least one electrode(preferably an electrode pair) is used a sensing electrode to detect theelectrical activity of target tissue (e.g., the vagus nerve).

In some embodiments, the stimulating electrode(s) is separate from thesensing electrode(s). In other embodiments, the same electrode canfunction both to stimulate and sense. Further still, some embodimentsinclude a combination of stimulation-only electrodes, sensing-onlyelectrodes, and combination stimulation and sensing electrodes. Thenumber of stimulation-capable, sensing-capable, and the total number ofelectrodes can be selected as desired for the given application. Anexample of an electrode suitable for coupling to a vagus nerve toprovide VNS therapy to a patient is disclosed in U.S. Pat. No.4,979,511, incorporated herein by reference. Mechanism 15 comprises anattachment mechanism that attaches the lead assembly 16 to the vagusnerve to provide strain relief and is described in U.S. Pat. No.4,979,511, incorporated herein by reference.

In addition to one or more electrodes attached to the patient's vagusnerve, one or more additional electrodes can also be provided andconnected to IMD 10. Such other electrodes can function as sensingelectrodes to sense any target parameter in the patient's body. Forexample, an electrode may be coupled to the patient's heart to sense theelectrical activity of the heart. Sensing electrodes may be additionallyor alternatively attached to other tissues of the body in addition to,or instead of, the patient's heart 17. In some embodiments, sensorsbesides electrodes can be included to sense various parameters of thepatient. The term “sensor” is used herein to encompass both electrodesand other types of sensing elements. Sensors used in conjunction withIMD 10 may comprise electrodes that sense an electrical signal (e.g., avoltage indicative of cardiac or brain wave activity), a pressuretransducer, an acoustic element, a photonic element (i.e., lightemitting or absorbing), a blood pH sensor, a blood pressure sensor, ablood sugar sensor, a body movement sensor (e.g., an accelerometer), orany other element capable of providing a sensing signal representativeof a physiological body parameter. Any of a variety of suitabletechniques can be employed to run a lead from an implantable devicethrough a patient's body to an attachment point such as the vagus nerveor cardiac or other tissue. In some embodiments, the outer surface ofthe IMD 10 itself may be electrically conductive and function as asensor as well. As will be explained below, in at least someembodiments, the IMD 10 comprises logic by which any two or more sensorscan be selected for operation with the IMD.

FIG. 1 also illustrates an external device implemented as a programmingsystem 20 for the IMD 10. The programming system 20 comprises aprocessing unit coupled to a wand 28. The processing unit 24 maycomprise a personal computer, personal digital assistant (PDA) device,or other suitable computing device consistent with the descriptioncontained herein. Methods and apparatus for communication between theIMD 10 and an external programming system 20 are known in the art.Representative techniques for such communication are disclosed in U.S.Pat. No. 5,304,206, and U.S. Pat. No. 5,235,980, both incorporatedherein by reference. As explained below, the IMD 10 includes atransceiver (such as a coil) that permits signals to be communicatedwirelessly between the wand 28 and the IMD 10. Via the wand 28, theprogramming system 20 generally monitors the performance of the IMD anddownloads new programming information into the device to alter itsoperation as desired. The programming system 20 can also cause the IMD10 to perform one or more calibration processes such as those describedbelow.

FIG. 2 shows a block diagram of a preferred embodiment of the IMD 10. Asshown, the IMD 10 includes a battery 30, a stimulation, sensing, andcommunication unit (“SSCU”) 32, and a controller 34. The SSCU 32 maycomprise, or be referred to as, a “pulse generator” or perform some orall of the functionality of a pulse generator. For example, under thecontrol of controller 34 the SSCU 32 may generate an electrical pulse tostimulate a neural structure in a patient. The battery 30 provides powerfor both by the SSCU 32 and the controller 34. As explained in greaterdetail with respect to FIG. 3, the SSCU 32 includes a voltage regulator58 that receives voltage from the battery 30 and provides operatingvoltage for use by the controller 34. In this way, the SSCU 32 cancontrol the voltage provided to the controller 34. The controller 34generally assists, controls, and/or programs the SSCU 32. Controller 34preferably comprises a processor such as a low-power, mixed-signalmicrocontroller, such as a processor available from Texas Instruments,Inc. as the MSP430F148 processor. Other suitable controllers may beused, although the processor preferably is capable of processing avariety of sensor inputs, uses low power, and operates at a high speed.In general, however, any suitable processor can be used to implement thefunctionality performed by the controller 34 as explained herein. Itwill be appreciated that some features of the controller 34 may also beprovided in whole or in part by the SSCU 32, and vice versa. Thus, whilecertain features of the present invention may be described as comprisingpart of the SSCU 32, it is not intended thereby to preclude embodimentsin which the features are provided by the controller. Likewise, certainfeatures described herein as comprising part of the controller 34 arenot intended to preclude embodiments in which the features comprise partof the SSCU 32.

FIG. 3 is a block diagram showing a preferred embodiment of the SSCU 32depicted in FIG. 2. Although a particular architecture for SSCU 32 isprovided in FIG. 3 and discussed more fully hereafter, the recitation ofa particular architecture is not intended to limit the scope of theinvention, which is limited only by the claims. The SSCU 32 comprises acurrent regulator 50, a voltage switch matrix 52, a register bank 54, atransceiver 56, a voltage regulator 58 (previously noted), a voltagereference 60, a pair of sense amplifiers 62 and 64, a reset detector 66,and a current switch matrix 68. The aforementioned components preferablyare coupled together on a single integrated circuit chip as shown, butmay also be implemented with other suitable architectures, includingindividual components or modules, although in general, integration ofthe components in a small number of modules increases reliability andreduces cost.

In accordance with the embodiment of FIG. 3, the register bank 54comprises eight control registers. Each register includes eight bits,and the function performed by each register in the FIG. 3 embodiment isdescribed below in Table I. The control registers are generally readableand writeable by the controller 34 to control the operation of the SSCU32. Control information provided by the controller 34 to the SSCU 32over the eight data lines (shown in FIG. 3 as “D[0-7]”) is latched, upondetection of a rising edge of the write enable (“WE”) signal, into theeight bits of the particular SSCU register that corresponds to theaddress provided on the three address signals (“A[0-2]”). Thus, thecontroller 34 is used to program the registers in the register bank 54by providing data to be written on the data lines D0-D7, an addresscorresponding to the target register on the address lines A0-A2, andthen asserting the WE signal to cause the target register to beprogrammed. Each of the eight registers is individually programmable bythis process. The register bank 54 also converts the register datareceived from the controller 34 into one or more digital signals thatare used by other components within the SSCU 32 as explained in greaterdetail below.

The eight registers of the register bank 54 are described below in TableI for a particular embodiment of the present invention.

TABLE I REGISTER DESCRIPTIONS Register Name Description General ControlControls the reset for the SSCU 32, bandgap trim for the senseamplifiers 62, 64 and trims for other functions Voltage Control Enablesand controls the amount voltage boost (50) for current control, controlscontroller power (58) Current Level Controls the current output level(50) Current Direction Designates which electrodes function as cathodeand anode for current pulse delivery (68), enables electrode dischargeand reed switch bypass Sense A Control Controls operation of sense amp A(62) Sense B Control Controls operation of sense amp B (64) Sense ASelect Selects positive and negative electrodes via switch matrix 52 forsense amp A (62) Sense B Select Selects positive and negative electrodesvia switch matrix 52 for sense amp B (64)

In preferred embodiments, the IMD 10 provides enhanced energyconservation by enabling two modes of operation for controller 34: afully operational mode of operation and a lower power, standby mode toconserve battery power. In the fully operational mode of operation, thecontroller 34 preferably performs some, or all, of the functionsdescribed herein. In the standby mode, the controller 34 generallyperforms fewer functions than in the fully operational mode. In someembodiments, other than perhaps refreshing any internal memory containedin the controller, the standby mode generally limits the controller towait for a transition to the fully operational mode. Because thecontroller is generally idle in the standby mode, battery power isconserved.

The controller 34 preferably includes, or otherwise accesses, are-programmable memory such as flash memory (implemented as non-volatilememory 40 in FIG. 2) that preferably stores the software to be executedby the controller 34. The voltage required for the controller 34 tore-program its flash memory may be different than the voltage needed forthe controller during other aspects of the fully operational mode. Thevoltage regulator 58 in the SSCU 32 receives voltage from the battery 30and provides supply voltage for the controller 34 in the fullyoperational and standby modes of operation, as well as for programmingflash memory contained in the controller.

The transceiver 56 generally permits the external wand 28 to communicatewith the IMD 10. More particularly, transceiver 56 permits the externalprogramming system 20 to program the IMD 10 (i.e., send programparameters to the IMD 10) and to monitor its configuration and state(i.e., query and receive signals from the IMD 10). In addition,transceiver 56 also permits the external programming system 20 (or thepatient alone by a suitable signaling means such as a magnet) to informthe implantable IMD 10 of the occurrence of a physiological event suchas a seizure.

In one embodiment, the SSCU 32 and the controller 34 preferably arereset on initial power-on or if the IMD simultaneously detects both amagnetic field and an RF transmission. Whenever a magnetic field isdetected by a Reed switch (not specifically shown) in the IMD 10, allcurrent switches within the VNS 10 are turned off as a safetyprecaution. This safety precaution can be temporarily overridden (i.e.,the IMD 10 may continue to generate and deliver electrical pulses tostimulating electrode 14) by writing an override bit in the CurrentDirection register (listed in Table I). To protect against a “stuck atoverride” failure, the aforementioned override bit preferably resetsitself after triggering an override time interval implemented by thereset detector 66.

The current regulator 50 delivers an electrical current programmed bythe controller 34 to the patient via lead 16 and stimulating electrodes12, 14. The IMD 10 preferably provides a constant current, used hereinto refer to providing a predetermined current or pulse shape that isindependent of he impedance across the leads (i.e., the impedancepresented by the patient's tissues). To overcome this impedance, thecurrent regulator 50 increases the battery voltage to a voltage that isdetermined by a value programmed into the Voltage Control register(Table I), while maintaining the current at a controlled magnitude. Themagnitude of the current delivered to the patient also is programmableby programming system 20 and controller 34 by writing a desired valueinto the Current Level register (Table I).

The current switch matrix 68 preferably provides current from currentregulator 50 to any desired sensor (e.g., electrodes) among thoseprovided in IMD 10 as programmed by the controller 34. Where electrodesare used as the sensing elements, a voltage signal from the selectedelectrodes is provided for conversion from analog to digital form by thecontroller 34 (which preferably has one or more internalanalog-to-digital converters 48, FIG. 2). The sense amplifiers 62 and 64are used to detect electrophysiologic signals preferably in any desiredfrequency range such as from 1 to 100 Hz. The voltage switch matrix 52connects the sense amplifiers 62 and 64 to any two or more selectableelectrodes. The controller 34 can program the Sense A Select and Sense BSelect registers in the register bank 54 to specify the particularsensor(s) that are selected to be coupled to each sense amplifier. Thesensors selected may comprise two or more sensors provided on a singlelead (e.g., lead 16, 18) or two or more sensors provided on differentleads. The selected sensors may also comprise a sensor provided on alead and an electrically conductive portion of the outer surface(sometimes referred to as the “can”) of the IMD 10, which may also beused as an electrode. Thus, in accordance with at least someembodiments, voltage switch matrix 52 and register bank 54 inconjunction with the controller 34, comprise sensor select logic 55which can be used to select any two or more sensors for sensing avoltage difference between the selected sensors.

The detection threshold of each sense amplifier 62, 64 is individuallyprogrammable, preferably in logarithmic steps, by the controller 34writing to the General Control register (Table I) of register bank 54.If a differential input signal exceeds the threshold, a digital outputis asserted by the connected sense amplifier. If not needed, the senseamplifiers can be switched off to a lower-power mode (also via theGeneral Control register).

Referring still to FIG. 3, in accordance with a preferred embodiment ofthe invention, the IMD 10 is capable of sensing two or more physiologicparameters via two or more of the electrodes (“EC[0-4]”). Although fiveelectrodes EC[0-4] are denoted in FIG. 3, it will be understood bypersons of skill in the art that any number of electrodes may beincluded for sensing a variety of physiological parameters. Sensors mayconnected to one or more of the SSCU's electrode connections EC[0-4]. Asdescribed above, the sensors may comprise any of the followingnon-limiting examples: electrodes that sense electrical activity, apressure transducer, an acoustic element, a photonic element, a blood pHsensor, a blood pressure sensor, a blood sugar sensor, or a bodymovement sensor. Accordingly, the sensors that are coupled to the IMD 10are capable of sensing one or more, and preferably two or more,physiological parameters selected from the following exemplary list: anaction potential in a nerve tissue, a heart parameter, a bodytemperature, a blood parameter (e.g., pH, pressure), and brain activity.The term “physiologic parameter” is intended to embrace all suchparameters whether they originate as electrical or non-electricalsignals. The controller 34 preferably programs the SSCU's register bank54 to sense whichever physiological parameters are desired for thepatient among the various sensors.

The sensed signals are received by the IMD 10 via one or more sensors.The controller 34 preferably programs the General Control register inthe register bank 54 to activate either or both of the sense amplifiers62 and 64 to receive signals from the sensors and/or electrodes. Thesignals from the sensors are routed via conductors 65, through thevoltage switch matrix 52 (programmed as explained above) and via thedifferential input conductors 67 and 69 to either or both of the senseamplifiers 62 and 64. The output signals 63 from the sense amplifiers 62and 64 are provided to the controller 34 and converted into digital formby an analog-to-digital converter (ADC) 48 in the controller as notedabove. The controller 34 then can analyze and process the receivedsignals in accordance with the programming of the controller asexplained below.

In some embodiments, the IMD 10 is programmed to deliver a stimulationtherapy (e.g., vagus nerve stimulation) at programmed time intervals(e.g., every five minutes) without regard to the physical condition ofthe patient, time of day, or other variables that may influence the needfor, and/or efficacy of, the stimulation. Such a treatment regimen isreferred to as “passive stimulation.” Alternatively or additionally, theimplantable IMD 10 may be programmed to initiate a therapeutic responseupon detection of a physiological event or upon another occurrence. Suchresponsive stimulation is referred to as “active stimulation.” As such,the IMD 10 delivers a programmed therapy to the patient based on signalsreceived from at least two sensors or based on at least two monitoredphysiological parameters. This disclosure is not limited to anyparticular type of physiological event. Non-limiting examples of aphysiological event include an epileptic seizure and a cardiacarrhythmia. The IMD 10 thus permits at least two physiologicalparameters to be sensed. Based on the physiological parameters sensed orsignals indicative of the sensed parameters, the IMD 10 performs ananalysis using an analysis module, typically comprising software and/orfirmware, to determine whether electrical neurostimulation is needed. Ifthe analysis module determines that electrical neurostimulation isneeded, then the IMD 10 provides an appropriate electrical pulse to aneural structure, preferably a cranial nerve. In the absence of a signalbased on analysis by the analysis module, either passive stimulation orno electrical neurostimulation may be provided.

Physiological parameters that provide an indication of the physiologicalevent generally vary from patient to patient. For example, actionpotentials on the vagus nerve during an epileptic seizure are detectableby measuring voltage fluctuations on the vagus nerve using a sensingelectrode pair. The measured voltage fluctuations may differ amongpatients experiencing the same type of seizure. Similarly, bodytemperature measurements during a seizure may differ among patienthaving the same type of seizure. Accordingly, the IMD 10 canadvantageously be adapted to the patient in which the IMD 10 isimplanted. As explained below, the IMD 10 of the present invention canbe customized to the particular patient's physiology to enable a moreaccurate physiologic event detection mechanism than might otherwise bepossible.

FIG. 4 illustrates a preferred method 80 for customizing the IMD 10 tothe patient in which the IMD is implanted. During routine operation, atblock 82 the controller 34 in the IMD 10 causes the IMD 10 todynamically acquire data representing one or more, and preferably two ormore, physiological parameters, such as those specified above.Dynamically acquiring physiological parameters comprises sensing thephysiological parameters with a sensor, generating a first set ofsignals representative of the physiological parameters sensed over afirst time period, and storing the first set of signals in a memory.Control logic is provided to facilitate the operation of the sensors,including the timing and sampling rate for each sensor. In block 84,method 80 further comprises informing the IMD 10 of the occurrence ofthe physiological event. This act includes determining when aphysiological event has occurred in the patient and providing anindication of the occurrence of the event. The determination of theoccurrence of the event may be made by the patient or a healthcareprovider, or automatically by, for example, a program analyzing EEG dataof the patient to confirm an epileptic seizure.

The IMD 10 may be informed of the physiologic event occurrence inaccordance with any suitable technique. For example, the patient (or ahealthcare provider) may inform the IMD 10 of the onset of thephysiologic event by way of a predetermined signal received from thewand 28 of the external programming system 20. If the patient is not inthe general vicinity of the external programming system when thephysiological event occurs, the patient may place an external device(e.g., a portable magnet) generally over the site of the IMD 10 totrigger a Reed switch inside the IMD, thereby signaling to the IMD thatthe event has occurred. In still other embodiments, the IMD 10 mayinclude an accelerometer that can detect a tap on the patient's skinover the site of the implanted IMD, and the event signal comprises theoutput signal from the accelerometer. In general, any mechanism by whichthe implanted IMD 10 can be informed of the occurrence of a physiologicevent is acceptable. In some embodiments, the IMD is informed of theoccurrence of the physiologic event at or near the beginning of thephysiological event, or during or even after the physiological event.

Referring still to FIG. 4, at block 86, controller 34 analyzes thestored first set of signals that correspond to a time period n. The timeperiod n can be any desired period of time but is preferably a period oftime preceding a physiological event. In some embodiments, n maycomprise any time period within a range of time periods such asapproximately a five minute period of time preceding the point at whichthe IMD was informed of the occurrence of the physiological event by oneof the methods previously described or other methods, such as the periodfrom five minutes prior to the signal informing the IMD of the eventuntil the signal itself. In another embodiment, the time period maycomprise the period from 30 minutes prior to the signal to the signal.In still other embodiments, more than one time domain may be examined,such as the five-minute period preceding the signal and the period fromone hour to 30 minutes preceding the signal. When only a single timedomain is examined, the time period n is preferably programmable, whichmay be accomplished by the controller 34 writing to the General Controlregister in the register bank 54. The controller 34 analyzes thepreviously stored physiological data during the time period according toan algorithm 89 that determines one or more “markers” that may beindicative of either a precursor to the physiological event, or thephysiological event itself. The markers may be unique to each patient.Such markers may include, but are not limited to, physiological datamagnitudes, physiological data timing, physiological data frequencycontent, physiological data variability, correspondence of physiologicaldata characteristics to stimuli, and combinations thereof. Once thecontroller 34 analyzes the stored physiological data and determines themarker(s) that are useful to detect future occurrences of thephysiologic event, in block 88 information characteristic of themarker(s) preferably is stored in memory in the controller 34 and usedto automatically detect future physiological event episodes byrecognition of sensed data similar to the markers.

In accordance with other embodiments, blocks 86 and 88 may be performedby an external device that analyzes the patient's previously storedphysiological data, such as a physiological event analysis programexecuting algorithm 89 in programming system 20. For example, in onesuch embodiment the implanted IMD 10 may be informed of the occurrenceof a physiological event as described above. Thereafter, rather thanhaving the implanted IMD itself determine the markers, the IMD maysimply record a timestamp in the stored physiologic data stream toindicate when the physiologic event occurred. Subsequently, programmingsystem 20 may upload the physiological data, including the physiologicalevent timestamps, from the implanted IMD 10, and analyze the data forthe time interval n prior to the timestamps, as described in blocks 86and 88 of FIG. 4. In this embodiment, the programming system 20 containsa program or logic (e.g., a processor executing suitable software) todetermine suitable markers for the patient based on the physiologicaldata uploaded from the patient. Programming system 20 can then be usedto download information corresponding to the determined markers into theimplanted IMD 10 for storage and subsequent use by the IMD itself todetermine future occurrences of the physiological event as exemplifiedin FIG. 5

FIG. 5 depicts a preferred method 90 for using the marker(s) generatedin method 80 of FIG. 4. In block 92, the method comprises sensing atleast two physiological parameters. In block 94, a second set (timeseries) of data is generated that is representative of the sensedparameters. This second set of data is then analyzed in block 96 todetermine the presence of the marker(s) generated previously (FIG. 4).If a marker is found in the second set of data, a nerve is stimulated inaccordance with a therapeutic response. The therapeutic response may beprogrammed into the IMD 10. In some embodiments, the IMD 10 may delivera first programmed therapy (e.g., a predetermined stimulation therapydelivered at preset time intervals (e.g., every five minutes). When amarker is detected in the second set of data, the first programmedtherapy can be delivered at that time rather than waiting for the nextscheduled time interval. In other embodiments, the detection of themarker may cause a second therapy to be delivered that may be differentthan the first therapy. The second therapy may be based on the firsttherapy, but with one or more parameters (e.g., pulse amplitude, pulseshape, duration, etc.) altered from the first therapy. The secondtherapy may be delivered instead of the first therapy for the nextscheduled interval (or more than one interval), or may be delivered inaddition to the first therapy, although it is preferred that delivery ofthe first and second therapies not overlap in time.

The IMD 10 can be operated to provide therapy for one or more of avariety of diseases, disorders, or conditions including, withoutlimitation, seizure disorders (e.g., epilepsy and Parkinson's disease),neuropsychiatric disorders including depression, schizophrenia, bi-polardisorder, borderline personality disorder, and anxiety, obesity, eatingdisorders including anorexia nervosa, bulimia, and compulsiveovereating, headaches (e.g., migraine headaches, neuromuscularheadaches), endocrine disorders (e.g., disorders of the pituitary gland,thyroid gland, adrenal system, or reproductive system includingpancreatic disorders such as diabetes and hypoglycemia), dementiaincluding cortical, sub-cortical, multi-infarct, Alzheimer's disease,and Pick's disease, pain syndromes including chronic, persistent orrecurring neuropathic or psychogenic pain, sleep disorders includingsleep apnea, insomnia and hypersomnia including narcolepsy, sleepwalking and enuresis, motility disorders (including hypermotility andhypomotility of the stomach, duodenum, intestines, or bowel), Crohn'sdisease, ulcerative colitis, functional bowel disorders, irritable bowelsyndrome, colonic diverticular disease, coma, circulatory and/orcoronary diseases (such as hypertension, heart failure, and heartbeatirregularities such as bradycardia and tachycardia).

In accordance with yet another embodiment of the invention, the IMD 10preferably is configurable to provide a programmable and suitabletherapy for any one or more diseases, disorders or conditions for whichthe IMD can provide therapy in response to sensed physiologicalparameters. At least some of the various medical problems that the IMD10 can be programmed to address are disclosed in any one or more of thefollowing United States patents, all of which are incorporated herein byreference: U.S. Pat. No. 4,702,254 (“Neurocybernetic Prosthesis”), U.S.Pat. No. 5,188,104 and U.S. Pat. No. 5,263,480 (“Treatment of EatingDisorders by Nerve Stimulation”), U.S. Pat. No. 5,215,086 (“TherapeuticTreatment of Migraine Symptoms by Stimulation”), U.S. Pat. No. 5,231,988(“Treatment of Endocrine Disorders by Nerve Stimulation”), U.S. Pat. No.5,269,303 (“Treatment of Dementia by Nerve Stimulation”), U.S. Pat. No.5,299,569 (“Treatment of Neuropsychiatric Disorders by NerveStimulation”), U.S. Pat. No. 5,330,515 (“Treatment of Pain by VagalAfferent Stimulation”), U.S. Pat. No. 5,335,657 (“Therapeutic Treatmentof Sleep Disorder by Nerve Stimulation”), U.S. Pat. No. 5,540,730(“Treatment of Motility Disorders by Nerve Stimulation”), U.S. Pat. No.5,571,150 (“Treatment of Patients in Coma by Nerve Stimulation”), U.S.Pat. No. 5,707,400 (“Treating Refractory Hypertension by NerveStimulation”), U.S. Pat. No. 6,026,326 (“Apparatus and Method forTreating Chronic Constipation”), U.S. Pat. No. 6,473,644 (“Method toEnhance Cardiac Capillary Growth in Heart Failure Patients”), U.S. Pat.No. 6,587,719 (“Treatment of Obesity by Bilateral Vagus NerveStimulation”), and U.S. Pat. No. 6,622,041 (“Treatment of CongestiveHeart Failure and Autonomic Cardiovascular Drive Disorders”). In thisembodiment, the IMD 10 is programmed to detect the onset of apredetermined physiological event associated with the medical problem orcondition afflicting the patient. The IMD 10 is also pre-programmed witha cranial nerve stimulation therapy, preferably a vagus nervestimulation therapy, suitable for the patient's affliction. One or moredetection modalities and therapeutic responses are described in one ormore of the aforementioned patents incorporated herein by reference.Further, the IMD 10 can be customized to the physiological symptomsmanifested by the patient as described above.

In still other embodiments, the IMD 10 can be programmed to providetherapy for a plurality of diseases, disorders, or conditions such asthose listed above. The IMD 10 in this embodiment comprises a sufficientnumber of sensors, preferably comprising electrode pairs, to senseparameters indicting physiological events associated with a plurality ofdiseases, disorders, or conditions (generally referred to hereinafter as“medical conditions”). In this embodiment, the IMD is adapted to sensephysiological parameters corresponding to a first physiological eventassociated with a first medical condition, and provide a suitablepre-programmed therapy in response (or prior to) the first physiologicalevent, and also to sense one or more other physiological parameterscorresponding to a second physiological event associated with a secondmedical condition, and provide a pre-programmed therapy suitable for thesecond medical condition. In this embodiment, the IMD may comprisecontroller 34 and SSCU 32. The controller 34 preferably is configurableto receive signals from a plurality of sensors, each corresponding toone or more physiological parameters indicative of one or morephysiological events associated with one or more medical conditionsexperienced by a patient. Further, the controller 34 preferably analyzessensor data to determine the impending onset of a physiological event(e.g., epileptic seizure, cardiac arrhythmia, indigestion, hunger, pain)and to cause the SSCU to provide a programmable therapy for each medicalcondition whose onset has been indicated (and/or diagnosed). Theprogrammable therapy for each condition may be stored in memory in thecontroller 34.

In accordance with another embodiment, FIG. 6 illustrates a method 100for a calibration process that adjusts the stimulation produced by theIMD 10 to achieve a first evoked response from tissue. In oneembodiment, IMD 10 comprises a neurostimulator for a cranial nerve(e.g., a vagus nerve) and the method comprises determining a firstthreshold that corresponds to minimum stimulation parameter settingssufficient to elicit a first evoked response from the cranial nerve.Minimum settings for stimulation parameters (e.g., current magnitude,frequency, pulse width, on-time and off-time) for the IMD 10 result ineliciting at least a first evoked response from the nerve whileconsuming relatively little power, or at least less power than for otherconfiguration settings. Because changes in any of a number ofstimulation parameters can affect the threshold for eliciting an evokedresponse, a number of “minimum settings” may be possible, as lowersettings for one parameter may be offset by a higher setting for anotherparameter. Because the IMD 10 preferably is implanted in the patient andthus run from a battery source, minimizing or reducing power consumptionis desirable to increase battery life.

The method of FIG. 6 illustrates a technique to determine the settingsfor the IMD 10 that cause the IMD to produce a stimulation that elicitsa first evoked response from the vagus nerve, preferably while reducingor minimizing power consumption. The IMD settings determined accordingto the method of FIG. 6 may be used to determine both desired andundesired evoked responses. A desired response may comprise, forexample, an evoked stimulation “floor” defining a “minimum parameter”set for stimulation of a cranial nerve such as a vagus nerve. Anundesired response may comprise a pain threshold at which the patientfeels pain resulting from the stimulation. Another undesired responsemay comprise retching by the patient. Responses such as pain or retchingthreshold are examples of stimulation “ceilings,” i.e., an upper limiton one or more stimulation parameters, above which patient tolerance isminimal or absent. Optimum settings between “floor” and “ceiling”settings may also be determined by the method of FIG. 6.

Referring still to FIG. 6, method 100 may be performed duringimplantation of the IMD 10 in the patient or after implantation during acalibration mode of operation as effectuated by, for example, theprogramming system 20. For example, the method may be performed afterimplantation of the IMD 100 to establish new parameter settings ifchanges in the nerve have resulted in changes in stimulation thresholdssuch as the “floor” and “ceiling” thresholds previously discussed. Atblock 102, the method comprises setting values for the stimulationparameters such as current level, frequency, duration, etc. In the IMD10 of FIG. 3, one or more of the parameters are programmable in the IMD10 via register bank 54. In at least some embodiments, the parametersset in block 102 preferably are initially set so as to cause the IMD toproduce a sufficiently low level of excitation energy to be unable toelicit an evoked response from the target vagus nerve.

Referring again to FIG. 6, in block 104 a stimulation is delivered bythe IMD 10 to the vagus nerve in accordance with the parameters set inblock 102. In decision block 106, the method determines whether anevoked response resulted from the stimulation of block 104. An evokedresponse can be determined via sensing electrodes placed on or near thevagus nerve and may either be distal to the stimulation electrodes orcomprise the stimulation electrodes themselves. In other embodiments,the sensing electrodes may be at a different location on the nerve, suchas in or near a final target region (e.g., the brain).

Regardless of the location of the sensing electrodes, IMD 10 receivesthe signals from the electrodes and determines whether an evokedresponse has occurred. The sensing data may be compared to a programmedthreshold that corresponds to a minimum signal that corresponds to aneffective induced action potential. The threshold may be based upon oneor more of the sensed signal amplitude, time delay since the stimulationpulse, and/or signal frequency content. Alternatively, the threshold maycomprise a minimum change in response to a stimulation change belowwhich a change in stimulation does not produce an effective change inaction potential. If an evoked response is determined to have occurred,then method 100 stops. Otherwise, the method comprises adjusting one ormore of the stimulation parameters at 108 and repeating the actions ofblocks 104 and 106. This process repeats itself until an evoked responseis detected. Once an evoked response is detected, the most recentsettings for the stimulation parameters are used to deliver futureneurostimulation therapy.

FIG. 7 shows a method 120 for a calibration process in which stimulationparameters are determined to achieve a stimulation “ceiling.” Inducedaction potentials on neurons within a nerve bundle such as the vagusnerve may increase as one or more stimulation parameter settings areincreased until all effective neurons are activated, after whichincreases in stimulation are not beneficial (and may be detrimental).Method 120 ensures that stimulation is not above this maximum level (the“ceiling”). At levels above the ceiling, the IMD would be wastingenergy, stimulating unwanted tissues, saturating desired tissues, and/orinducing discomfort or other unacceptable responses in the patient.Method 120 may be performed during implantation of the IMD 10 in thepatient or after implantation during a calibration mode of operation aseffectuated by, for example, the programming system 20.

After a stimulation is delivered at 122, a decision is made at 124 todetermine whether the ceiling has been reached or exceeded. If theceiling has been reached or exceed, the process stops. If the ceilinghas not been reached or exceeded, the method comprises at 126 the stepof adjusting one or more stimulation parameters (e.g., currentmagnitude, frequency, duration, etc.) and looping back to block 122.Once the process stops, the most recent settings for the stimulationparameters are used to deliver future neurostimulation therapy.

FIG. 8 shows a method 130 for a calibration process in which stimulationparameters are determined to target one or more specific types orsub-types of fibers within a nerve bundle. The vagus nerve, for example,comprises multiple nerve fibers (A fibers, B fibers, C fibers). Bytargeting one or more particular fibers for stimulation, and converselynot targeting one or more other fiber types, efficacy ofneurostimulation therapy may be improved and/or side effects may bereduced. Different fiber types have different characteristics in theiraction potentials. As a result, the stimulation-induced actionpotentials may be monitored to determine what is being stimulated.Accordingly, method 130 permits the IMD 10 to be configured to adjustthe stimulation to increase or maximize excitation of targeted fibertypes, and/or reduce or minimize excitation of untargeted fiber types.In one nonlimiting example, stimulation parameters may be selected tostimulate only type A fibers, and avoid (or at least minimize)stimulation of type B and C fibers. Method 130 may be performed duringimplantation of the IMD 10 in the patient or after implantation during acalibration mode of operation as effectuated by, for example, theprogramming system 20. The programming system 20 can cause thecalibration process of FIG. 8 to be performed for a specific fiber typeas selected by a user of the programming system.

Referring again to FIG. 8, a stimulation is delivered to the nerve at132. After the stimulation is delivered, a decision is made at 134 todetermine whether action potentials have been induced in the targetfiber type. This determination can be made in accordance with any of avariety of techniques. Any one or more of the following characteristicscan be monitored using the sensing electrodes to determine whether thetarget fiber type has been excited: time delay from stimulation todetected excitation, time duration of the action potential, andfrequency content of the action potential. A specific threshold, whichmay comprise a measured voltage response profile in the nerve over atarget time interval following stimulation, can be set for any of theaforementioned characteristics and a comparison of the nerve signal tothe thresholds can be made to determine whether the target fiber typehas been excited. The specific thresholds used in this analysis may beset according to the specific fiber types being targeted. Accordingly,the thresholds may vary from application to application.

If the target fiber type(s) has been excited, the process stops. If thetarget fiber type(s) has not been excited, then at 136 the methodcomprises adjusting one or more stimulation parameters (e.g., currentmagnitude, frequency, duration, etc.) and looping back to block 132. .Once the process stops, the most recent settings for the stimulationparameters are used to deliver future neurostimulation therapy.

FIG. 9 shows a method 140 for a calibration process in which stimulationparameters are determined to provide a first, desired evoked response intarget tissue while not producing a second, undesired response in othertissue (“untargeted” tissue). For example, it may be desired to induceaction potentials on the patient's vagus nerve, but not to stimulateother tissue such as the patient's vocal cords. Thus, electrodes may beplaced on or adjacent the targeted tissue (e.g., the vagus nerve) andthe untargeted tissue (e.g., the vocal cords) and the method 140 of FIG.9 can be performed to permit the IMD 10 to be configured to adjust thestimulation to produce the first, desired response in the targetedtissue, but not produce the second, undesired response in the untargetedtissue. Method 140 may be performed during implantation of the IMD 10 inthe patient or after implantation during a calibration mode of operationas effectuated by, for example, the programming system 20.

Referring again to FIG. 9, a stimulation is delivered to the targetedtissue at 142. After the stimulation is delivered, a decision is made at144 to determine whether the targeted tissue has been excited (i.e.,whether the first, desired evoked response has occurred). Thisdetermination can be made in accordance with any of a variety oftechniques, such as those described above involving sensing of thetargeted tissue such as a cranial nerve. If the targeted tissue has notbeen excited, then at 146 the method comprises adjusting one or morestimulation parameters (e.g., current magnitude, frequency, duration,etc.) and looping back to block 142 and repeating blocks 142, 144, and146 until the targeted tissue is excited by the delivered stimulation.

Once the IMD 10 has been configured to excite the targeted tissue, themethod continues at decision 148 to determine whether the untargetedtissue has been excited. If the untargeted tissue is not excited, thenthe method 140 stops. If, however, the untargeted tissue is excited bythe delivered stimulation at 142, the method comprises at 150 adjustingone or more stimulation parameters (e.g., current magnitude, frequency,duration, etc.) and looping back to block 142 to repeat the processuntil the stimulation parameters are set so that targeted is excited,but untargeted tissue is not excited. The parameters set as a result ofthe method of FIG. 9 are used to operate the IMD to provide futureneurostimulation therapy.

Determining whether the untargeted tissue is excited may comprise thesame or similar techniques implemented to determine whether the targetedtissue is excited, such as determining whether a sensed voltagethreshold is exceeded in for the untargeted tissue, or by the patient ora healthcare provider manually signaling to the device (using, e.g., amagnet) whether or not the untargeted tissue has been excited. In someembodiments, the method of FIG. 9 achieves a configuration for the IMDthat causes the IMD to excite targeted tissue, but not excite untargetedtissue. In other embodiments, the configuration causes the IMD to excitetargeted tissue, but reduce the excitation of untargeted tissue.

FIG. 10 shows a method embodiment 180 in which the IMD 10 stimulates anerve (e.g., a cranial nerve such as the vagus nerve) based on theintrinsic electrical activity of the nerve. The intrinsic electricalactivity of the nerve comprises the activity of the nerve other thanelectrical activity induced by an artificial stimulus such as thatprovided by the IMD 10, i.e., it is the electrical activity native tothe patient. Stimulating based on sensed intrinsic electrical activityof the nerve can be used to block such intrinsic signals. Stimulatingbased on the intrinsic electrical activity of the nerve may be used toenhance the therapeutic benefit of neurostimulation therapy. Forexample, at least some afferent intrinsic signals from various parts ofthe body may interfere with vagus nerve stimulation. Blocking suchintrinsic signals may increase the efficacy of vagus nerve stimulationprovided by the IMD 10, which may induce “extrinsic” action potentialson the nerve. “Blocking” such intrinsic signals may comprise reducingthe amplitude of, or completely eliminating the signals. Alternatively,a vagus nerve stimulator may be more effective when its stimulation isdelivered during periods of low or high intrinsic activity on the vagusnerve. The IMD 10 of the preferred embodiment can be configured to sensea patient's intrinsic nerve signals and (a) to provide stimulation toblock afferent or efferent intrinsic nerve signals, (b) to providestimulation during periods of low intrinsic activity, and/or (c) toprovide stimulation during periods of high intrinsic activity. Theprogramming system 20, for example, can be used to dictate the desiredresponse—(a), (b), or (c).

Referring again to FIG. 10, at 182, the method comprises sensing theintrinsic electrical activity of the nerve. The method further comprisesanalyzing the sensed intrinsic activity, as depicted at 184 of FIG. 10.Analysis of the sensed intrinsic activity may comprise storing theintrinsic signals over a first time interval and analyzing those signalsby a software algorithm to determine whether stimulation from the IMD 10should be applied to the nerve. Following the analysis of the intrinsicactivity, a decision is made at 186 as to whether or not the IMD 10should deliver stimulation to the nerve. If no stimulation is desired,the method ends. If stimulation is desired, the method comprisesstimulating in response to, or in anticipation of, the intrinsicelectrical activity of the nerve, as illustrated as 188 of FIG. 10. Thestimulation produced at 184 may be used to block the intrinsic activityon the nerve from reaching the brain or to increase the efficacy ofvagus nerve stimulation as noted above.

In accordance with at least some embodiments of the invention, the IMD10 may comprise any or more or all of: a stimulation delivery module, asignal capture module, an adjustment module, and an increment module. Insome embodiments, the stimulation module may deliver an electricalsignal from a pulse generator (discussed above) to a nerve. The signalcapture module may determine whether a first evoked neural response hasoccurred on the nerve as a result of the stimulation. The adjustmentmodule may adjust one or more of the plurality of stimulation parametersif the first evoked response has not occurred. The increment module maycause the stimulation delivery, signal capture and increment modules torepeat their operations until the first evoked neural response occurs.These, or other modules, may perform any of the functions describedherein. The various modules are implemented in software, firmware,hardware, or any suitable combination thereof.

While the preferred embodiments of the present invention have been shownand described, modifications thereof can be made by persons skilled inthe art without departing from the spirit and teachings of theinvention. The embodiments described herein are exemplary only, and arenot intended to limit the scope of protection provided herein.

What is claimed is:
 1. An implantable neurostimulator, comprising: apulse generator that provides an electrical pulse signal to stimulate acranial nerve in a patient; a stimulation lead assembly coupled to saidpulse generator for delivering said electrical pulse signal to saidcranial nerve, said lead assembly having a proximal end coupled to saidpulse generator and a distal end comprising a stimulation electrodeassembly coupled to said cranial nerve; and a plurality of sensorelements coupled to said pulse generator and that sense at least twophysiological parameters selected from the group consisting of an actionpotential in a nerve tissue, a heart parameter, a temperature, a bloodparameter, and brain wave activity.
 2. The implantable neurostimulatorof claim 1, wherein at least one of said plurality of sensor elementscomprises an electrode and a second of said plurality of said sensorelements is selected from the group consisting of an electrode, athermocouple, a pressure transducer, an acoustic transducer, and aphotonic element.
 3. The implantable neurostimulator of claim 1, whereinone of said plurality of sensor elements comprises a nerve electrodethat senses an action potential in a nerve tissue.
 4. The implantableneurostimulator of claim 3, wherein said nerve electrode is adapted tocouple to a vagus nerve of the patient for sensing action potentialstraveling along said vagus nerve.
 5. The implantable neurostimulator ofclaim 4, wherein said nerve electrode does not comprise part of saidstimulation electrode assembly.
 6. The implantable neurostimulator ofclaim 1, further comprising: a controller that receives and analyzessignals representative of said at least two physiological parameters;and said pulse generator generates said electrical pulse stimulationsignal in response to an analysis by said controller of said signalsrepresentative of said at least two physiological parameters.
 7. Animplantable neurostimulator, comprising: a pulse generator that providesa therapeutic electrical pulse signal to a nerve in a patient; astimulation lead assembly coupled to said pulse generator for deliveringsaid electrical pulse to said nerve, said lead assembly having aproximal end coupled to said pulse generator and a distal end comprisinga stimulation electrode assembly coupled to said nerve; a plurality ofsensor elements coupled to said pulse generator for sensing at least twophysiological parameters selected from the group consisting of an actionpotential in a nerve tissue, a heart parameter, a temperature, a bloodparameter, and brain wave activity, each of said sensor elements adaptedto provide a sensor signal representative of at least one physiologicalparameter; and a controller that receives and analyzes sensor signalsfrom at least two of said sensor elements; wherein said pulse generatorgenerates said therapeutic electrical pulse signal in response to saidanalysis by said controller.
 8. The implantable neurostimulator of claim7, wherein said pulse generator also delivers a therapeutic electricalpulse signal at predetermined intervals
 9. A method of providingelectrical neurostimulation therapy to a patient, comprising: receivingsensor signals from at least two sensors in a patient; performing ananalysis based on said at least two sensor signals to determine whetherelectrical neurostimulation is needed; and providing an electrical pulseto a nerve in the patient when it is determined that electricalneurostimulation is needed.
 10. The method of claim 9 further comprisingprogramming at least one register in an implantable neurostimulator toselect said at least two sensors that are to be used for receivingsensor signals.
 11. The method of claim 9 further comprising providingan electrical pulse to the nerve at programmable time intervals.
 12. Amethod of providing electrical neurostimulation therapy to a patient,comprising: sensing at least two physiological parameters selected fromthe group consisting of voltage fluctuations in a nerve tissue, a heartparameter, a temperature, a blood parameter, and brain wave activity;performing an analysis based on said at least two sensed physiologicalparameters to determine whether electrical neurostimulation is needed;and providing an electrical pulse to a nerve in the patient when it isdetermined that electrical neurostimulation is needed.
 13. The method ofclaim 12 further comprising providing an electrical pulse to the nerveat programmable time intervals.
 14. A method, comprising: sensingintrinsic electrical activity on a cranial nerve of a patient; andstimulating the cranial nerve based on the sensed intrinsic electricalactivity.
 15. The method of claim 14 wherein stimulating the nervecomprises blocking intrinsic electrical activity from reaching theperson's brain.
 16. The method of claim 14 wherein the cranial nerve isa vagus nerve and stimulating the nerve increases the efficacy of vagusnerve stimulation.
 17. An implantable neurostimulator, comprising: apulse generator that provides an electrical pulse signal to a cranialnerve in a patient, said pulse generator being programmable to define aplurality of stimulation parameters that characterize said signal; astimulation lead assembly coupled to said pulse generator for deliveringsaid electrical pulse signal to said cranial nerve, said lead assemblyhaving a proximal end coupled to said pulse generator and a distal endcomprising a stimulation electrode assembly coupled to said cranialnerve; a sensing electrode assembly coupled to said pulse generator andsaid cranial nerve that senses electrical activity on said cranialnerve; and control logic that causes said cranial nerve to be stimulatedbased on said sensed intrinsic electrical activity on said cranialnerve.
 18. The implantable neurostimulator of claim 17 wherein thecontrol logic causes the nerve to be stimulated to block intrinsicelectrical activity of said cranial nerve.
 19. The implantableneurostimulator of claim 17 wherein the control logic causes the nerveto be stimulated to increase the efficacy of vagus nerve stimulation.